WO 00/14183 and U.S. Pat. No. 6,103,099 to ExxonMobil teach a process for producing an isoparaffinic lubricant base stock which comprises hydroisomerizing a waxy, paraffinic, Fischer-Tropsch synthesized hydrocarbon feed comprising 650-750° F.+hydrocarbons, said hydroisomerization conducted at a conversion level of said 650-750° F.+feed hydrocarbons sufficient to produce a 650-750° F.+hydroisomerate base stock which comprises said base stock which, when combined with at least one lubricant additive, will form a lubricant meeting desired specifications. Hydraulic oils are claimed, but nothing is taught regarding processes to make or compositions of lubricating oils having excellent oxidation stability.
Conoco ECOTERRA™ Hydraulic Fluid is formulated with high quality hydrocracked base oils and fortified with an ashless, zinc-free antiwear additive package. It has a high oxidation stability, such that the ISO 32 grade has a result of 700 minutes in the rotary pressure vessel oxidation test (RPVOT) by ASTM D 2272 at 150° C. The ISO 46 grade has a result of 685 minutes, and the ISO 68 grade has a result of 675 minutes. Conoco ECOTERRA™ Hydraulic Fluid, however has a low viscosity index of about 102 or less.
PetroCanada PURITY™ FG AW Hydraulic Fluids have RPVOT results of between 884 and 888 minutes, but they too only have viscosity indexes of about 102 or less.
PetroCanada HYDREX SUPREME™ is an ISO 32 hydraulic fluid with a RPVOT result of about 1300 minutes. HYDREX SUPREME™ is a trademark of PetroCanada. The base oil in this product is a highly refined water-white base oil. The base oil used in the PetroCanada HYDREX SUPREME™ hydraulic fluid does not have a viscosity index that is exceptionally high, and the base oil is available in limited quantities. It is blended with a significant amount of viscosity index improver to provide it with a viscosity index of about 353. Additionally, hydraulic fluids having high viscosity indexes and good oxidation stabilities have been made from synthetic base oils, and also from high oleic base oils made from vegetable oils. These types of base oils, however, are expensive and not available in large quantities.
What is desired is a lubricating oil having excellent oxidation stability and high viscosity index made using a base oil having greater than 90 wt % saturates, less than 10 wt % aromatics, a viscosity index greater than 120, less than 0.03 wt % sulfur and a sequential number of carbon atoms, without the inclusion of high levels of viscosity index improvers; and a process to make it.